Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For example, in an optical disk drive, the head will typically include a mirror and objective lens for reflecting and focusing a laser beam on to a surface of the disk.
In a modern magnetic hard disk drive device, each head is a sub-component of a head gimbal assembly (HGA) that typically includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit (FPC) that includes a flex cable. The plurality of HGAs are attached to various arms of the actuator, and each of the laminated flexures of the HGAs has a flexure tail that is electrically connected to the FPC of the HSA.
In magnetic recording applications, the head will typically include a transducer having an inductive writer and a magnetoresistive reader. The head may read and write data on a surface of one of a plurality of co-rotating disks that are co-axially mounted on a spindle motor. Magnetically-written transitions are thereby laid out in concentric circular tracks on the disk surface. In modern disk drives, the tracks must be extremely narrow and the transitions closely spaced to achieve a high density of information per unit area of the disk surface. Still, the disks must rotate quickly so that the computer user does not have to wait long for a desired bit of information on the disk surface to translate to a position under the head.
The required close spacing of data written on the disk surface has consequences on the design of the disk drive device and its mechanical components. Among the most important consequences is that the magnetic transducer on the head must operate in extremely close proximity to the magnetic surface of the disk. However, because there is relative motion between the disk surface and the head due to the disk rotation and head actuation, continuous contact between the head and disk can lead to tribological failure of the interface. Such tribological failure, known colloquially as a “head crash,” can damage the disk and head, and cause data loss. Therefore, the magnetic head is typically designed to be hydrodynamically supported by an extremely thin air bearing so that its magnetic transducer can operate in close proximity to the disk while physical contacts between the head and the disk are minimized or avoided.
The head-disk spacing present during operation of modern hard disk drives is extremely small—measuring in the tens of nanometers. Obviously, for the head to operate so closely to the disk, the head-disk interface must be kept clear of debris and contamination—even microscopic debris and contamination. Tribological problems in magnetic disk drives sometimes have non-obvious causes that, once known, understood, and accounted for, give one disk drive manufacturer a competitive edge over another. In addition to tribological consequences, contamination and debris at or near the head disk interface can force the head away from the disk. The resulting temporary increases in head-disk spacing cause magnetic read/write errors. Accordingly, magnetic hard disk drives are assembled in clean-room conditions and the constituent parts are subjected to pre-assembly cleaning steps during manufacture.
In many disk drives, the actuator arm (or arms) that positions the head(s) extends from an actuator body that is fixed to an actuator pivot bearing by a tolerance ring. Typically, tolerance rings include a cylindrical base portion and a plurality of contacting portions that are raised or recessed from the cylindrical base portion. The contacting portions are typically partially compressed during installation to create a radial preload between the mating cylindrical features of the parts joined by the tolerance ring. The radial preload compression provides frictional engagement that prevents axial slippage of the mating parts. For example, in disk drive applications, the radial compressive preload of the tolerance ring prevents separation and slippage at the interface between the actuator arm body and the pivot bearing during operation and during mechanical shock events. The tolerance ring also acts as a radial spring. In this way, the tolerance ring positions the interior cylindrical part relative to the exterior cylindrical part while making up for radial clearance and manufacturing variations in the radius of the parts.
State of the art tolerance rings are typically manufactured from a flat metal sheet with stamping, forming, rolling, and other steps to provide raised or recessed contacting regions and a final generally-cylindrical shape. Installation of the tolerance ring involves axial motion relative to a generally cylindrical hole in an exterior part (e.g. actuator arm) and/or relative to a generally cylindrical inner part (e.g. actuator pivot bearing). Such tolerance ring installation may shear metal fragments from either the actuator arm body or an outer surface of the actuator pivot bearing cartridge, and such fragments can later contaminate the head-disk interface and ultimately lead to a head crash and possibly to data loss.
The actuator arm structure is typically fabricated from aluminum or an alloy of aluminum and is therefore typically softer and more easily scratched by the tolerance ring than is the actuator pivot bearing cartridge, which may be fabricated from stainless steel. Still, the tolerance ring may scrape the outer surface of the actuator pivot bearing during installation, even if the actuator pivot bearing cartridge is fabricated from stainless steel. Consequently, the installation of a conventional tolerance ring is somewhat prone to generate debris.
Most state-of-the-art attempts to improve cleanliness of disk drive components have focused on pre- and post-assembly cleaning steps and on environmental cleanliness during assembly. Assembly in clean environments also does not eliminate or remove contaminates and debris thoroughly. Less frequently, disk drive designers consider the generation of debris and contamination earlier in the design of sub-components. Still, such consideration is often restricted to the selection of lubricants and adhesives. Consequently, there remains much scope in the art for reducing debris generation via novel changes to the basic design or assembly of various sub-components of the disk drive.
Therefore, there is a need in the art for a tolerance ring design and/or tolerance ring fabrication method that can reduce the creation of debris during disk drive assembly. Although the need in the art was described above in the context of magnetic disk drive information storage devices, the need is also present in other applications where a tolerance ring is used in a clean environment that must remain as free as possible of debris and contaminants.